1. Field of the Invention
The present invention relates to a spin transistor using a spin-orbit coupling induced magnetic field, and more particularly, to a spin transistor having a wide ON/OFF operation margin and making less noise that is generated by leakage magnetic field.
2. Description of the Related Art
A metal oxide silicon field effect transistor (MOSFET) is one of representative elements in a modern integrated circuit technology. The MOSFET is generally included as an essential element for performing ON/OFF switching operation in a memory device such as a flash memory and a DRAM, as well as a logic circuit, ASIC and a microprocessor. Recently, a spin transistor (Spin-FET) is introduced. A conventional semiconductor based transistor controls only electric charge formed in the semiconductor using electric field. On the contrary, the spin transistor simultaneously controls electric charge and its spin. The spin transistor can be used in a switching element and a logic circuit by control of spin-polarized charge.
Though the MOSFET is currently used as an essential element in a semiconductor field, it has several drawbacks. For example, it is difficult to further reduce power consumption and volume of the MOSFET. In addition, the gate oxide of the MOSFET faces physical limitations. In order to overcome such limitations of the MOSFET, transistors that control spin-precession of electric charge with the voltage are introduced. Among them, a spin transistor includes a source, a drain and a channel connecting the source and the drain. A quantum well layer may be used as the channel in the spin transistor.
In a conventional spin transistor, magnetization directions of a source and a drain are identical to a channel direction, that is, a traveling direction of an electron (refer to Datta-Das spin FET in Applied physics letter, vol. 56, 665, 1990, and U.S. Pat. No. 5,654,566 issued to Mark B. Johnson entitled “MAGNETIC SPIN INJECTED FIELD EFFECT TRANSISTOR AND METHOD OF OPERATION”). In the conventional spin transistor, spin information of the electron is likely to be lost by stray field generated at the ends of the source and the drain. The generated stray field shortens an effective distance of spin transfer and makes considerable noise.
The conventional spin transistor controls a spin direction of an electron reached at the drain to be parallel or anti-parallel to the magnetization direction of the drain by controlling a “spin-precession” of an electron. By control of the spin-precession of the electron, the resistance of the channel is adjusted. However, it is very difficult to precisely adjust an angle of the precession and to accurately form the channel to have a proper length corresponding to the precession angle. Therefore, the conventional spin transistor has a narrow ON/OFF operation margin and allows a narrow process margin for the channel length. As a result, operating accuracy degrades and a manufacturing process thereof becomes complicated.